Sheet metal forming has been used in the industry for years for creating metal parts from a blank sheet metal, for example, automobile manufacturers and their suppliers produce many of the parts using sheet metal forming. One of the most used sheet metal forming processes is referred as draw forming or stamping. Cross-section view of an exemplary deep draw stamping set up is shown in FIG. 1. To create a part or product, it involves a hydraulic or mechanical press pushing a specially-shaped die 110 onto a matching punch 130 with a piece of blank sheet metal 120 or workpiece in between. The blank 120 is initially supported by a binder 108 and/or the punch 130. The binder 108 is sometimes referred to as binder ring, ring or blank holder, which is situated on top of a die cushion 106 that is actuated by air, oil, rubber or springs 107. Exemplary products made from the sheet metal forming process include, but are not limited to, car hood, fender, door, automotive fuel tank, kitchen sink, aluminum can, etc. In deep drawing, the depth of a part or product being made is generally more than half its diameter. As a result, the blank 120 is stretched and therefore thinned in various locations due to the geometry of the part or product. The part or product is only good when there is no structural defect such as material failure (e.g., cracking, tearing, wrinkling, necking, etc.).
In certain situations, severe metal forming conditions may be encountered (e.g., narrow high gradient portion near window opening of a car door). To alleviate such severe forming condition, a technique is referred to as lancing operation is used. In lancing operation, a cut is made to a scrap portion of a blank sheet metal 120 near an area subject to severe forming condition. Lancing route or path of a lancing cut is generally a smooth curve (e.g., straight line, open curve, etc.). At many instances, the lancing cut is made gradually in time as the blank 120 being pressed by the punch 130. This is referred to as progressive lancing operation. As shown in FIG. 1, a sloped lance or knife 111 is disposed on the die face and a corresponding slot 112 on the punch 130 to achieve such a lancing operation. The height (H1) 115 of the knife 111 is adjustable so that the start of a lancing cut can be achieved at various distances of the die 110 from the position of being fully closed with the punch 130. This height can be fully determined using the numerical simulation. Two examples of lancing route are shown in FIG. 2. In the first sheet metal part 202, there is a scrap area 212 with a straight-line lancing route 222. In the second part 204, there is another scrap area 214 with a curved-line lancing route 224. Other lancing route such as a closed curve can also be used.
With advent of computer technology, manufacturing procedure of a product can be numerically simulated using computer aided engineering analysis (e.g., finite element analysis (FEA)). FEA is a computerized method widely used in industry to model and solve engineering problems relating to complex systems such as three-dimensional non-linear structural design and analysis. FEA derives its name from the manner in which the geometry of the object under consideration is specified. With the advent of the modern digital computer, FEA has been implemented as FEA software. Basically, the FEA software is provided with a model of the geometric description and the associated material properties at each point within the model. In this model, the geometry of the system under analysis is represented by solids, shells and beams of various sizes, which are called elements. The vertices of the elements are referred to as nodes. The model is comprised of a finite number of elements, which are assigned a material name to associate the elements with the material properties. The model thus represents the physical space occupied by the object under analysis along with its immediate surroundings. The FEA software then refers to a table in which the properties (e.g., stress-strain constitutive equation, Young's modulus, Poisson's ratio, thermo-conductivity) of each material type are tabulated. Additionally, the conditions at the boundary of the object (i.e., loadings, physical constraints, etc.) are specified. In this fashion a model of the object and its environment is created.
FEA has been using for numerically simulating manufacturing process of sheet metal forming to ensure formability (i.e., the sheet metal forming setup suitable for producing a part that meets the criteria). However, prior art approaches do not simulate progressive lancing operation properly. For example, prior art approaches often result into a distorted lancing route due to finite elements near the lancing route are allowed to freely deform after the initial lancing cut. As a result, the numerically simulated lancing route has a zigzag line. Furthermore, in additional to the distorted deformed FEA mesh, extremely small finite elements may be created. As a result, the numerically simulation either fails due to numerical error in processing such elements or becomes very length due to the size of such elements to maintain numerical stability.
Therefore, it would be desirable to have improved methods and systems for conducting a time-marching simulation of manufacturing a sheet metal part that requires progressive lancing operation (PLO).